For many years it has been the common practice to install ventilators in openings in building walls to provide for the flow of ventilating air through the enclosed crawl space beneath the floor of the building. In recent years, foundation ventilators have been provided with shutters which are thermostatically controlled so that they remain in an open position during warm weather when the temperature is above about 70.degree. F., and the shutters move to a closed position when the outside temperature drops below a predetermined amount, such as 40.degree. F. This type of automatic foundation ventilator is disclosed in U.S. Pat. No. 3,528,606.
U.S. Pat. No. 4,274,330 discloses an automatic ventilator of this general type which includes a rectangular mounting frame that is first mounted in the foundation opening and the shutter support housing is then positioned in and fixed to the mounting frame. U.S. Pat. No. 4,587,892 discloses another automatic ventilator in which the mounting frame and the housing supporting the operating shutters are of molded plastic construction and are preassembled. The automatic ventilator of this patent is mounted in the wall opening in such a manner that the ventilator remains firmly seated in the opening with any expansion or contraction of the ventilator during use.
It has been the common practice to preassemble the molded plastic shutter support housing and the mounting cover frame of the ventilator of U.S. Pat. No. 4,587,892 by integrally molding openings in the outwardly extending flange of the shutter support housing and molding mounting pins on the mounting cover frame to extend into and through the openings in the shutter support housing. The ends of the molded pins extending through the openings are then heated and flattened to fix the shutter support housing to the mounting cover frame. If the ventilator does not operate properly after it has been assembled in this manner, it is very difficult, if not impossible, to separate the shutter support housing and the mounting cover frame to carry out the required repairs or adjustments to the shutter operating mechanism, with the result that the entire automatic ventilator must be discarded.